Uploaded by Tracey Rigby

07 coacervate formation lab

Coacervate Formation Lab
Evolution and the origin of life are not necessarily parts of the same process. Mechanisms operating when life
came into existence may be quite different than the mechanisms which cause and control evolution. In
addition, every indication is that life began billions of years ago, left little if any evidence of the process (no
"molecular fossils"), except living organisms, and has not taken place since. In contrast, evolution (which
provides an explanation for the diversity of life) has left fossil indicators of past lives, and shows every
indication of going on today and into the future. Therefore, evolution is much easier to study, with an
abundance of various types of evidence. With the continuation of research going on today, we may indeed
eventually have enough circumstantial evidence to describe a plausible scenario for how life began.
Under certain conditions, proteins, carbohydrates and other materials in a solution can come together to form
irregular volumes bounded by a membrane-like interface to the surrounding medium. These organized
clusters of droplets are called coacervates, and they have some of the properties of living cells. Consequently,
such structures may represent one of the early stages in the origin of life. In this activity, you can produce
coacervates, study the conditions under which they form, and observe some of their life-like properties.
Under suitable conditions, life-like structures can form naturally from relatively simple materials.
The origin of life on earth did not necessarily involve supernatural processes.
Briefly explain why are we doing this lab? What are we trying to do?
1. What is a coacervate?
2. How do the materials you used to make coacervates compare with those that might have been present in
the ancient oceans?
3. Draw and title a picture of a coacervate into your lab book.
 safety goggles
 compound microscope
 slides
 cover slips
 test tube rack with clean small culture tubes (13x100 mm works well)
 one medicine dropper per tube
 one dropping bottle with 0.1M HCl solution
 pH paper in dispenser with color code
 One 50-ml beaker with coacervate mix (5 parts of 1% gelatin soln + 3 parts 1% gum arabic soln.)
Summarize the steps below into your lab book
1. Put on safety goggles.
2. Half fill a tiny test tube with the pre-made mix of a 5:3 ratio of gelatin and gum arabic. Note that the mix is
clear; there are no coacervates in the mix.
3. Using short thin straw, transfer a tiny drop to pH paper, record this initial pH in a table.
4. Carefully add one drop acid (0.1M HCl) from a dropping bottle. Cover the mouth of the test tube with
parafilm and turn it upside down so the acid mixes gently with the "Mix". If it doesn't get real cloudy,
repeat. Should require no more than one or two drops of acid. Cloudiness indicates presence of
5. When cloudy, use short plastic straw to transfer one drop to pH paper, and one drop to a clean microscope
slide. Read and record pH in a table.
6. Place a cover slip on the drop, and observe under the microscope. Look for coacervates (see example
above). Note: a small diaphragm opening works best for this.
7. When you find good coacervates, sketch a few in your lab book.
8. After sketching coacervates, add another drop of acid to mix in test tube, turn it upside down to mix it in,
and repeat until the extreme cloudiness disappears, and the mix becomes relatively clear again (should
take only 2-3 additonal drops of acid to do this). When this happens, check and record the pH. Observe if
you have the time (coacervates should be gone).
Create a data table in which you record:
 The number of drops of HCl added (first entry should be 0 drops)
 The pH of the mixture
 The appearance of the mixture (clear or cloudy)
Also include the titled sketch of your coacervate.
1. How do coacervates differ, and how are they similar to living cells?
2. What role might have been played by coacervates or similar structures before life began?
3. What characteristics would coacervates have to exhibit to be considered living?
You can make the 1% solns day before lab, (adding a pinch of mold inhibitor seems to help). Mix the two solutions (5:3
ratio) day of lab, then dispense into little beakers. For 5 classes, 500 ml of gelatin solution and 300 ml of gum arabic
solution should be ample. Gelatin is a protein; gum arabic is a carbohydrate. For current sources of Gum Arabic, see
Resources, below. Gelatin can be purchased in grocery stores, or from most school chemical supply catalogs.